James Van Der Beek Reveals He Got Vasectomy Before Cancer Diagnosis

James Van Der Beek says he and his wife are completely done having kids ... admitting he went under the knife and got a vasectomy -- right before he was diagnosed with cancer.

The actor sat down for an interview with People -- published Saturday -- where he talked about his family life ... including the huge brood of kids he shares with his wife of more than a decade, Kimberly.

James says the couple -- who has six kids -- has been blessed with great fertility ... and, they know the only way to ensure they were finished on the kids front was for James to have a doctor snip him down there.

VDB says he told his kids to be careful when they ran up to him after the surgery ... telling the little ones they could seriously hurt him if they ran and smacked him in the crotch.

He says his youngest daughter, six-year-old Gwen, said -- with all sincerity -- that she hopes his "vagina feels better" ... a pretty cute, if anatomically incorrect, statement.

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Of course, James and his family are going through the wringer right now ... with the "Dawson's Creek" star telling People he has colorectal cancer.

James says he's receiving treatment for the disease and he's hopeful things will get better. He did say initially finding out about the Stage 3 cancer diagnosis was shocking ... adding he feels much better that he's able to discuss it openly now.

Van Der Beek will appear in "The Real Full Monty" -- a two-hour special where he and other big stars will strip down to raise awareness about certain types of cancer -- next month.